I bow to your research. What I know is the length of the rolls to play one 3.5 minute song was 21 ft. On average and that would be a size easily packed for shipping and handling for the merchandisers and allowed the roll to be read at a speed comfortable for all piano players of the time. Believe me I am no authority on this and if it is incorrect I would enjoy knowing the real deal. Post your Site and a link to your book again that is allowed here and it sounds like a rich and rewarding read.